Reginald T. Rex

This character is available for download here.

I would like to share a solution I've come up with for the legs of this character. After rigging the leg using the 'reverse foot' setup I commonly use, it was immediately obvious that it wouldn't be sufficient for this character. In a reverse foot rig, the ankle stays in place as the leg moves, since it is usually resting on the ground. However for a T-rex, the ankle is in the air, so having it stay stationary while the character is positioned did not feel natural at all.

The solution is something I've decided to call the 'Dual IK Reverse Leg' because that is exactly what it is. Two bone chains are used for the IK setup. On one, a single solver runs through all 3 leg bones (ankle, shin, thigh), which creates the single chain behaviour for the length of the leg. On the other, 2 IK solvers are applied, but in reverse... one on the thigh with the knee as the target, and one on the ankle with a chain length of two (ankle, shin). The knee target is parented to the knee bone of the single chain leg, and the ankle pole target is parented to the foot control. The result is a 3 bone leg, solved all at once with independent control of the ankle and knee!

Here is a blend file demonstrating both techniques so you can see the difference for yourself. The ankle bone is likely to flip if the foot control is rotated forward too far, but since the ankle target is accessible to the animator, I don't feel it is a problem - you can just grab it and move it back.